1. Field of the Invention
This invention pertains generally to electrical switching apparatus and, more particularly, to such apparatus including trip circuits, such as microprocessor-based trip circuits. The invention also relates to arc fault or ground fault circuit interrupters, such as, for example, receptacles.
2. Background Information
Ground fault circuit interrupters (GFCIs) include, for example, ground fault circuit breakers, ground fault receptacles and cord mounted ground fault protection devices. GFCIs and arc fault current interrupters (AFCIs) are well known in the art. Examples of ground fault and arc fault circuit breakers are disclosed in U.S. Pat. Nos. 4,081,852; 5,260,676; 5,293,522; 5,892,593; and 5,896,262.
The U.S. Consumer Product Safety Commission (CPSC) and the circuit protection industry are concerned with AFCI and GFCI devices failing without the consumer knowing that there is no corresponding arc fault or ground fault protection. As AFCI and GFCI safety and protection requirements become relatively more complex, a microprocessor-based solution becomes more necessary. However, the microprocessor, as a result of its complexity, is generally the most likely component of a well-designed electrical switching apparatus to fail, when the other components are not overstressed.
Many AFCI/GFCI manufacturers employ a mechanical lockout approach, but this requires the use of a test button or a trip event. See, for example, U.S. Pat. Nos. 6,040,967 (a resettable GFCI receptacle including a reset lockout mechanism to prevent the resetting of electrical connections between input and output conductors if the circuit interrupting mechanism used to break the connection is non-operational or if an open neutral condition exists); U.S. Pat. No. 6,829,124 (a GFCI is automatically tested for functionality when it is reset, but cannot be reset if the fault circuit interrupter circuitry is not operational); and U.S. Pat. No. 6,867,954 (a reverse wiring protection device for a GFCI cannot be reset when the line and load are miswired). For example, if a failure of the tripping circuit or the sensing circuit is detected, then the corresponding circuit interrupter cannot be closed. This leaves the consumer with a power outage that cannot be corrected without an electrician. This power loss will be a disincentive to test circuit interrupters. Therefore, there is a likelihood that fewer circuit interrupters will be tested and potentially more failed circuit interrupters will remain in the field.
It is known to employ a self test approach using a microprocessor, but this depends upon the very element that is most likely to fail. See, for example, U.S. Pat. Nos. 6,807,035; and 6,807,036.
It is also known to only indicate failure, but not trip. See, for example, U.S. Pat. No. 6,744,254.
It is known to employ a “watchdog” circuit to continually monitor the status of a microcomputer of a circuit breaker. If the “watchdog” circuit fails to receive a pulse signal from the microcomputer at regular intervals, then it attempts to reset the microcomputer. See, for example, U.S. Pat. No. 5,311,392. See, also, U.S. Pat. Nos. 5,822,165; 6,262,871; 6,330,141.
U.S. Pat. No. 4,539,618 discloses a digitally controlled overload relay which monitors current flow in a circuit and triggers an electromagnetic interrupter to open the circuit upon detection of an overcurrent condition. For normal current conditions, a microprocessor generates a train of pulses which is received by the electromagnetic interrupter for maintaining the circuit closed. The pulse train is terminated upon detection of an overcurrent condition.
There is room for improvement in electrical switching apparatus, such as arc fault or ground fault circuit interrupters, and receptacles.